1. Field of the Invention
This invention relates to circular saw and bandsaw machines, and incorporates a method of controlling the rate at which the work is presented to the saw blade, plus a method for monitoring, displaying, and controlling the performance of the saw blade within predetermined levels of stability by altering the feed rate.
2. Description of the Prior Art
Circular saw and bandsaw machines have long been used as economical means for cutting wood, metal, and other materials. In recognition of the high costs for raw material and labor, automatic/computer control of work feed rates and sawing accuracy becomes of paramount importance. Optimized automatic control of work feed rates and saw blade stability keeps material and production costs down. The use of thinner saw blades and smaller rough sawn dimension sizes can conserve natural resources in the wood products industry, and reduce material waste in all industries which use circular saw and bandsaw machines in the manufacturing process. In the lumber industry, current production methods result in a larger than necessary amount of waste in order to manufacture finished dimension lumber. Reduction of this waste requires the solution of several technical problems.
The first problem is the rate at which the work is fed into the saw blade. The work is either manually or automatically fed into these sawing machines. In manually fed machines, the operator listens to the sound of the saw blade and varies the feed rate by judgement, frequently not realizing that the saw blade is being overfed. Sawing machines having automatic feed systems, use predetermined feed rates as a function of thickness of work (depth of cut). These predetermined feed rates do not consider any variable except depth of cut. This automatic feed system permits overfeeding and in some cases underfeeding of the saw machine, resulting in erratic lateral movement of the saw blade and loss of control of the saw line. Slower than optimum feed rates are required to compensate for the variable densities of wood encountered from summer to winter, density changes within the same log, partially frozen logs, and the sharpness of the saw blade cutting teeth. These variables all require on-line adjustments to work feed rates.
The second problem is the target size of the rough sawn work, which must be maintained large enough so that finished lumber is not undersized. This excess material, which is later removed to produce finish dimension lumber, represents waste. Uncontrolled lateral deviations in the saw lines during the cutting operation require larger rough sawn target sizes. These saw blade movements have several causes: mis-alignment of saw blade guides, normal saw blade tooth wear, bending or uneven dulling of saw teeth, and knots in the saw log. These typical conditions can cause lateral instability of the saw blade, with resultant deviations of the saw line.
The third problem is offsetting of the saw blade from the desired saw line. If the saw teeth are dulled by sand, gravel or other foreign objects embedded within the work, the saw blade can be thrust to one side for the entire length of the cut, offsetting the saw line from a minor deviation of 0.005 to a major of 0.080 of an inch. When a saw blade runs in an offset condition and encounters a knot, or is substantially over-fed, it is possible for the saw blade to run completely out of the work. This ruins the saw blade tension, requiring hours of bench work to bring the saw back into proper tension so that it will again cut straight and accurately. The saw blade could also disintegrate, destroying itself and surrounding equipment, thus requiring down time to repair the damage. The safety of personnel is also placed in jeopardy if the saw blade disintegrates.
The fourth problem is the width of the saw cut, or kerf. Reduction of the saw blade gauge/thickness, and of side clearance, (the distance the tooth extends beyond the side of the saw blade body), decreases the width of the kerf. Heavier gauges and larger side clearance are currently used to protect the saw from the instability effects of excessive feed rates.
The fifth problem encompasses other considerations that directly affect optimized cutting efficiency, such as saw blade design, saw blade strain, and guide pressure.
At the present time, these considerations are being addressed by using larger rough sawn lumber target sizes, thicker saw blades, and larger kerf dimensions. Numerous attempts through the years have been made to solve these problems, with varied success.
1. Saw blade strain devices such as weight and lever or high strain pneumatic systems have improved saw blade performance. Some improvement in saw blade stability has been obtained, and higher feed rates achieved.
2. The use of pressure guides provides an additional increment of saw blade stability. These devices are commonly used in the wood products industry.
3. A control system utilizing the saw blade sagging angle in the direction of the work feed was the basis for U.S. Pat. No. 4,437,367 which was issued to Karl Hauser. This system works well in small bandsaw machines, but will not function adequately with the larger bandmill machines which have wider saw blades. This patent applies to bandsaw machines that hinge and move to the work in lieu of the work feed system common in larger sawing machines in which the work is fed into the machine.
4. Utilizing the pressure imposed by the work on the back of the saw blade to control work feed rates, as in U.S. Pat. No. 3,680,417 issued to John R. Wells, has merit when using small bandmill machines which use throw-away saw blades. Large bandsaw machines have blade widths exceeding two inchs, and the same problems exist with this patent as with the saw blade sagging angle control system.